#include <bits/stdc++.h>
//#include <atcoder/all>
using namespace std;
//using namespace atcoder;
//using mint = modint1000000007;
//const int mod = 1000000007;
//using mint = modint998244353;
//const int mod = 998244353;
//const int INF = 1e9;
//const long long LINF = 1e18;
#define rep(i, n) for (int i = 0; i < (n); ++i)
#define rep2(i,l,r)for(int i=(l);i<(r);++i)
#define rrep(i, n) for (int i = (n-1); i >= 0; --i)
#define rrep2(i,l,r)for(int i=(r-1);i>=(l);--i)
#define all(x) (x).begin(),(x).end()
#define allR(x) (x).rbegin(),(x).rend()
#define endl "\n"
#define P pair<int,int>
template<typename A, typename B> inline bool chmax(A & a, const B & b) { if (a < b) { a = b; return true; } return false; }
template<typename A, typename B> inline bool chmin(A & a, const B & b) { if (a > b) { a = b; return true; } return false; }

int main() {
	ios::sync_with_stdio(false);
	cin.tie(nullptr);
	int n; cin >> n;
	vector<int>a(n), b(n);
	rep2(i, 1, n) {
		cin >> a[i] >> b[i];
	}
	int ans = 0;
	rep2(i, 0, 37 * 10101) {
		int sa = i;
		rep2(j, 1, n)sa += a[j];
		int sb = 0;
		rep2(j, 1, n)sb += b[j];
		int j = sa - sb;
		a[0] = i;
		b[0] = j;
		if (j < 0)continue;
		bool chk = true;
		rep(k, n) {
			if (sa < a[k] + b[k])chk = false;
		}
		if (chk)ans++;
	}
	cout << ans << endl;
	return 0;
}